One of the steps in the manufacturing of integrated circuits is called "probe". After the finished processing of a wafer, the wafer has to be tested with a probe card at a prober station in order to electrically test the performance of each die before it is packaged. At this point, die that fail in probe are marked as defective and ultimately discarded. A die can fail for a number of reasons. One such cause of failure could be due to hardware failure, when the die in fact could be perfectly good.
A prober provides a means for a die in a wafer to make electrical contact with a probe card which is connected to test hardware. Currently, probe cards have a number of probe tips that contact either bond pads peripherally or bumps in array form on a die. It is often necessary for the probe tips to scrape an oxidation layer off the bond pad or bump in order to make electrical contact. This requires a certain probe tip force and an X and/or Y motion.
With today's level of integration, dies and corresponding probe cards need to make a large number of contacts. Several hundred simultaneous contact are not uncommon. One result is that probe cards contain large numbers of probe tips, each of which must make contact with the corresponding target peripheral bond pads or array bumps. Unfortunately however, it is possible that different probe tips in a given probe card will provide different contact force to the corresponding bonding pads or bumps. This results in unequal electrical contact to the die. It would be advantageous to be able to detect this problem, resolve it, and verify that it has been resolved. Currently, there is an inability to measure probe tip force on a per probe tip basis in "real time" when a probe card is installed in a probe station (where real time refers to a mid-test interrupt). It would also be advantageous if the probe tip force could be measured and translated to a spring constant as an integrated part of the probe process.
Currently, Applied Precision Inc. of Mercer Island, Wash. manufactures an off-line station capable of measuring relative force of individual probe tips. As the station is off-line, measuring and testing probe tip force cannot be integrated into the production flow.